This proposal is a request for a new electron microscope to replace an obsolete electron microscope for which parts are no longer manufactured. This shared instrument is essential to the on-going research of 10 investigators in the Departments of Pathology and Medicine at the Beth Israel Hospital. These investigators are currently funded by a total of 20 grants from the NIH as well as several grants from other agencies. Much of the work supported by these grants is dependent on the successful collection of electron microscopic data. This is no longer possible with the instrument we wish to replace. Research topics to be supported by the proposed new instrument fall broadly into a number of interrelated categories. These include basophil and mast cell biology, tumor biology, eosinophil biology, platelet and coagulation biology, macrophage biology, endothelial cell biology, parasitology, secretion, lipid body biochemistry and biology, inflammation and repair, immediate and cell-mediated immunity, and the development of ultrafast and fast microwave energy-assisted fixation methods for electron microscopy.